Light-emitting diode and method for manufacturing tunnel junction layer

ABSTRACT

A light-emitting element layer  10  includes: an n-type contact layer  11 ; a first light-emitting layer  12 ; a tunnel junction layer  13 ; a second light-emitting layer  14 ; and a p-type contact layer  15  laminated in this order. The first light-emitting layer  12  and the second light-emitting layer  14  emit light of the same wavelength. The tunnel junction layer  13  includes: a p-type tunnel layer  131  made of AlGaAs containing p-type impurities (C); and an n-type tunnel layer  133  made of GaInP containing n-type impurities (Te). A highly n-type impurities-doped layer  132  having a higher concentration of n-type impurities than the n-type tunnel layer  133  is arranged between the p-type tunnel layer  131  and the n-type tunnel layer  133.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC § 119 fromJapanese Patent Application No. 2017-103197 filed May 25, 2017 andJapanese Patent Application No. 2018-017456 filed Feb. 2, 2018.

BACKGROUND Technical Field

The present invention relates to a light-emitting diode and a method formanufacturing a tunnel junction layer.

Related Art

A light-emitting diode has been widely known that includes a p-typesemiconductor layer containing p-type impurities, an n-typesemiconductor layer containing n-type impurities, and an active layersandwiched between the p-type semiconductor layer and the n-typesemiconductor layer and having a smaller band gap than the p-typesemiconductor layer and the n-type semiconductor layer.

Japanese Patent Application Laid-Open Publication No. 2009-522755discloses a light-emitting diode that includes a firstradiation-generating active layer and a second radiation-generatingactive layer being arranged one above another in a vertical direction.The first radiation-generating active layer includes a p-typesemiconductor layer, an active layer (a radiation-generating layer) andan n-type semiconductor layer, and emits incoherent light. The secondradiation-generating active layer includes a p-type semiconductor layer,an active layer (a radiation-generating layer) and an n-typesemiconductor layer, and emits light of a similar wavelength to that ofthe first radiation-generating active layer. The light-emitting diodefurther includes a tunnel junction layer formed between the firstradiation-generating active layer and the second radiation-generatingactive layer.

By adopting a configuration where plural light-emitting parts arelaminated one above another across a tunnel junction layer, a forwardcurrent can be supplied to the plural light-emitting parts connected inseries across the tunnel junction layer. This enables each of the plurallight-emitting parts to emit light.

However, adopting this configuration may reduce light emission output ofthe light-emitting diode because, in some cases, a part of the lightemitted from each light-emitting part cannot be extracted to the outsideof the light-emitting diode.

An object of the present invention is to improve light emission outputof a light-emitting diode that is composed of plural light-emittingparts being laminated one above another across a tunnel junction part.

SUMMARY

According to an aspect of the present invention, a light-emitting diodeincludes: a first light-emitting part including a first p-type layer, afirst n-type layer, and a first active layer, the first p-type layercontaining a compound semiconductor and p-type impurities, the firstn-type layer containing a compound semiconductor and n-type impurities,the first active layer containing a compound semiconductor and beingsandwiched between the first p-type layer and the first n-type layer; asecond light-emitting part including a second p-type layer, a secondn-type layer, and a second active layer, the second p-type layercontaining a compound semiconductor and p-type impurities, the secondn-type layer containing a compound semiconductor and n-type impurities,the second active layer containing a compound semiconductor and beingsandwiched between the second p-type layer and the second n-type layer,the second light-emitting part emitting light of the same wavelength asthe first light-emitting part; and a tunnel junction part including athird p-type layer and a third n-type layer, the third p-type layerfacing the first p-type layer and containing Al_(x)Ga_(1-x)As (0≤x≤0.3)and p-type impurities, the third n-type layer facing the second n-typelayer and containing (Al_(x)Ga_(1-x))_(y)In_(1-y)P (0≤x≤0.2, 0.4≤y≤0.6)and n-type impurities, the tunnel junction part being sandwiched betweenthe first light-emitting part and the second light-emitting part, thethird p-type layer and the third n-type layer forming a tunnel junction.

In the light-emitting diode, the tunnel junction part further includes ahighly n-type impurities-doped layer at a boundary between the thirdp-type layer and the third n-type layer, the highly n-typeimpurities-doped layer containing n-type impurities at a higherconcentration than the third n-type layer.

Further, the highly n-type impurities-doped layer is thinner than thethird n-type layer and the third p-type layer.

Further, concentration of the n-type impurities in the highly n-typeimpurities-doped layer is not less than 1×10²⁰ cm⁻³ and not more than1×10²¹ cm⁻³.

Further, concentration of the n-type impurities in the third n-typelayer is higher at a side facing the third p-type layer than at a sidefacing the second n-type layer.

Further, concentration of the p-type impurities in the third p-typelayer is higher at a side facing the third n-type layer than at a sidefacing the first p-type layer.

Further, both of the first active layer and the second active layer havea single- or multi-quantum well structure including a well layer and abarrier layer, the well layer is composed of(Al_(x)Ga_(1-x))_(y)In_(1-y)As_(z)P_(1-z) (0≤x≤0.2, 0.7≤y≤1.0,0.7≤z≤1.0), and the barrier layer is composed ofAl_(x)Ga_(1-x)As_(z)P_(1-z) (0≤x≤0.3, 0.7≤z≤1.0).

Further, each of the first p-type layer, the second p-type layer and thethird p-type layer contains C as p-type impurities, and each of thefirst n-type layer, the second n-type layer and the third n-type layercontains Te as n-type impurities.

According to another aspect of the present invention, a light-emittingdiode includes: a first light-emitting part including a first p-typelayer, a first n-type layer, and a first active layer, the first p-typelayer containing Al, Ga, As and p-type impurities, the first n-typelayer containing Al, Ga, As and n-type impurities, the first activelayer containing a group III-V semiconductor and being sandwichedbetween the first p-type layer and the first n-type layer; a secondlight-emitting part including a second p-type layer, a second n-typelayer, and a second active layer, the second p-type layer containing Al,Ga, As and p-type impurities, the second n-type layer containing Al, Ga,As and n-type impurities, the second active layer containing a groupIII-V semiconductor and being sandwiched between the second p-type layerand the second n-type layer, the second light-emitting part emittinglight of the same wavelength as the first light-emitting part; and atunnel junction part including a third p-type layer and a third n-typelayer, the third p-type layer facing the first p-type layer andcontaining Ga, As and p-type impurities, the third n-type layer facingthe second n-type layer and containing Ga, In, P and n-type impurities,the tunnel junction part being sandwiched between the firstlight-emitting part and the second light-emitting part, the third p-typelayer and the third n-type layer forming a tunnel junction.

In the light-emitting diode, the third n-type layer has a larger bandgap than the third p-type layer.

Further, the first p-type layer and the second n-type layer have acommon composition except for contained impurities.

Further, each of the third p-type layer and the third n-type layer iscomposed of a direct band gap semiconductor.

Further, concentration of the n-type impurities in the third n-typelayer is not less than 1×10²⁰ cm⁻³ and not more than 1×10²¹ cm⁻³.

According to still another aspect of the present invention, a method formanufacturing a tunnel junction layer using organic vapor phasedeposition, includes: a first process that supplies a first material gascontaining a group III element, a second material gas containing a groupV element, and a third material gas containing a dopant of a firstconductivity type, onto a compound semiconductor layer on which thetunnel junction layer is to be laminated; a second process that stopssupplying the first material gas, the second material gas and the thirdmaterial gas, and supplies a fourth material gas containing a dopant ofa second conductivity type opposite to the first conductivity type; anda third process that continues to supply the fourth material gas, andfurther supplies a fifth material gas containing a group III element anda sixth material gas containing a group V element.

In the method for manufacturing a tunnel junction layer, the firstmaterial gas contains Al and Ga as group III elements, the secondmaterial gas contains As as a group V element, the third material gascontains C as a dopant of the first conductivity type, the fourthmaterial gas contains Te as a dopant of the second conductivity type,the fifth material gas contains Ga and In as group III elements, and thesixth material gas contains P as a group V element.

Further, the compound semiconductor layer on which the tunnel junctionlayer is to be laminated contains Al, Ga, and As.

Further, the first process increases a flow rate of the third materialgas with a lapse of time, and the third process decreases a flow rate ofthe fourth material gas with a lapse of time.

Further, a temperature of an object on which the tunnel junction layeris to be laminated is lowered by 100 C° to 150 C° before starting thefirst process, and, after finishing the third process, the temperatureof the object on which the tunnel junction layer has been laminated isincreased by 100 C° to 150 C°.

According to the present invention, it is possible to improve lightemission output of a light-emitting diode that is composed of plurallight-emitting parts being laminated one above another across a tunneljunction part.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention will be described indetail based on the following figures, wherein:

FIG. 1 is a diagram illustrating a cross-sectional structure of asemiconductor layer forming substrate according to the exemplaryembodiment;

FIG. 2 is a diagram illustrating a structure around a tunnel junctionlayer of the semiconductor layer forming substrate;

FIG. 3 is a flowchart illustrating a method for manufacturing thesemiconductor layer forming substrate;

FIG. 4 is a timing chart illustrating a method for manufacturing thetunnel junction layer;

FIG. 5 is a diagram illustrating a cross-sectional structure of asemiconductor light-emitting element including a light-emitting elementlayer;

FIG. 6 is a flowchart illustrating a method for manufacturing thesemiconductor light-emitting element;

FIG. 7 is a diagram illustrating a relationship between a forwardcurrent and a light emission output of the semiconductor light-emittingelements of the Example 1 and the Comparative Example;

FIG. 8 is a diagram illustrating a relationship between a light emissionoutput and a forward voltage of the semiconductor light-emittingelements of the Examples 1 and 2;

FIG. 9A is a TEM picture of the tunnel junction layer of the Example 1;

FIG. 9B is a TEM picture of the tunnel junction layer of the Example 3;

FIG. 10 is a diagram illustrating a relationship between forwardvoltages of the semiconductor light-emitting elements of the Examples 1and 3; and

FIG. 11 is a diagram illustrating the results of secondary ion massspectroscopy (SIMS) of the tunnel junction layers of the Examples 1 and3.

DETAILED DESCRIPTION

Hereinafter, the exemplary embodiment according to the present inventionwill be described in detail with reference to attached drawings. Itshould be noted that size, thickness, etc. of the parts in the drawingsto be referred to in the following description may differ from actualdimensions. It should also be noted that, in the following description,group III-V semiconductors consisting of three or more elements may bereferred to with the composition ratio of each element being omitted(e.g. “AlGaInAsP”).

<Structure of the Semiconductor Layer Forming Substrate>

FIG. 1 is a diagram illustrating a cross-sectional structure of thesemiconductor layer forming substrate 1 according to the exemplaryembodiment.

The semiconductor layer forming substrate 1 includes: a growth substrate1 a; and a light-emitting element layer 10 that is composed of pluralsemiconductor layers laminated on the growth substrate 1 a and emitslight by passing a current. Although details are described later, thelight-emitting element layer 10 functions as a so-called double-stackedlight-emitting diode, which is formed by stacking plural light-emittinglayers (light-emitting diodes) each having a p-n junction, andarranging, between the light-emitting layers, a tunnel junction layer (atunnel diode) that passes a current in a reverse direction (from ann-type layer to a p-type layer) by a tunnel effect.

[Growth Substrate]

The growth substrate 1 a of the exemplary embodiment is composed of asingle crystal of a compound semiconductor (a group III-Vsemiconductor). For example, the growth substrate 1 a of this kind maybe GaAs and InP.

[Light-Emitting Element Layer]

The light-emitting element layer 10 includes: an n-type contact layer 11laminated on the growth substrate 1 a; a first light-emitting layer 12laminated on the n-type contact layer 11; a tunnel junction layer 13laminated on the first light-emitting layer 12; a second light-emittinglayer 14 laminated on the tunnel junction layer 13; and a p-type contactlayer 15 laminated on the second light-emitting layer 14. Hereinafter,components of the light-emitting element layer 10 will be described oneby one.

(N-Type Contact Layer)

The n-type contact layer 11, in which electrons are carriers, is a layerfor providing an n-electrode (not shown; a negative electrode portion30; see FIG. 5 described later). The n-type contact layer 11 of theexemplary embodiment is composed of a compound semiconductor (a groupIII-V semiconductor) that lattice-matches a surface (growth surface) ofthe growth substrate 1 a.

The n-type contact layer 11 is preferably doped with n-type impurities.Containing n-type impurities at a concentration of 5×10¹⁷ cm⁻³ to 2×10¹⁹cm⁻³ is preferable in that an increase in resistance can be preventedand deterioration of crystallinity is less likely to occur. The n-typeimpurities may be, but not limited to, Te, Si or Se.

(First Light-Emitting Layer)

The first light-emitting layer 12, which is an example of the firstlight-emitting part, has a so-called double hetero junction and aquantum well structure, and emits light by passing a current.

The first light-emitting layer 12 of the exemplary embodiment includes:a first n-type cladding layer 121 laminated on the n-type contact layer11; a first active layer 122 laminated on the first n-type claddinglayer 121; and a first p-type cladding layer 123 laminated on the firstactive layer 122. Further, the first active layer 122 includes pluralfirst well layers 1221 and plural first barrier layers 1222 alternatelylaminated on each other.

[First n-Type Cladding Layer]

The first n-type cladding layer 121, which is an example of the firstn-type layer, injects carriers (holes and electrons) into the firstactive layer 122 and confines the carriers, together with the firstp-type cladding layer 123. The first n-type cladding layer 121 of theexemplary embodiment is composed of a compound semiconductor (a groupIII-V semiconductor) that lattice-matches the n-type contact layer 11.

The first n-type cladding layer 121 preferably has a larger band gapthan the n-type contact layer 11.

Further, the first n-type cladding layer 121 is preferably doped withn-type impurities. Containing n-type impurities at a concentration of5×10¹⁷ cm⁻³ to 1×10¹⁹ cm⁻³ is preferable in that carriers are moreeffectively injected into the first active layer 122 having a quantumwell structure, and light absorption by carries within the first n-typecladding layer 121 can be reduced. Here, the first n-type cladding layer121 preferably contains the same n-type impurities as the n-type contactlayer 11.

[First Active Layer]

The first active layer 122 emits light through recombination of holesand electrons. The first active layer 122 of the exemplary embodimenthas a so-called multi-quantum well (MQW) structure formed by alternatelystacking the first well layers 1221 and the first barrier layers 1222.Note that the first active layer 122 (the first well layers 1221 and thefirst barrier layers 1222) basically does not contain n-type impuritiesand p-type impurities. However, during the manufacturing of the firstactive layer 122, n-type impurities and p-type impurities may bediffused from the first n-type cladding layer 121 and the first p-typecladding layer 123, respectively, to the first active layer 122.

{First Well Layer}

The first well layer 1221, which is an example of the well layer, issandwiched by two adjacent first barrier layers 1222. However, in thisexample, the first well layer 1221 located lowermost in the figure (atthe side of the first n-type cladding layer 121) is sandwiched by thefirst n-type cladding layer 121 and the first barrier layer 1222. Also,in this example, the first well layer 1221 located uppermost in thefigure (at the side of the first p-type cladding layer 123) issandwiched by the first p-type cladding layer 123 and the first barrierlayer 1222. Accordingly, in this example, the number of the first welllayers 1221 is larger than the number of the first barrier layers 1222by one. The first well layer 1221 of the exemplary embodiment iscomposed of a compound semiconductor (a group III-V semiconductor) thatlattice-matches the first n-type cladding layer 121 and the first p-typecladding layer 123. The first well layer 1221 is preferably composed of(Al_(x)Ga_(1-x))_(y)In_(1-y)As_(z)P_(1-z) (0≤x≤0.2, 0.7≤y≤1.0,0.7≤z≤1.0). Also, the first well layer 1221 is preferably composed of adirect band gap compound semiconductor (group III-V semiconductor).

The first well layer 1221 preferably has a smaller film thickness thanthe first n-type cladding layer 121 and the first p-type cladding layer123. Additionally, the first well layer 1221 preferably has a smallerband gap than the first n-type cladding layer 121 and the first p-typecladding layer 123.

{First Barrier Layer}

The first barrier layer 1222, which is an example of the barrier layer,sandwiches the first well layer 1221 together with an adjacent firstbarrier layer 1222. The first barrier layer 1222 of the exemplaryembodiment is composed of a compound semiconductor (a group III-Vsemiconductor) that lattice-matches the first well layer 1221. The firstbarrier layer 1222 is preferably composed of Al_(x)Ga_(1-x)As_(z)P_(1-z)(0≤x≤0.3, 0.7≤z≤1.0). Also, the first barrier layer 1222 is preferablycomposed of a direct band gap compound semiconductor (group III-Vsemiconductor).

The first barrier layer 1222 preferably has a smaller film thicknessthan the first n-type cladding layer 121 and the first p-type claddinglayer 123. Also, the first barrier layer 1222 preferably has a largerfilm thickness than the first well layer 1221. Additionally, the firstbarrier layer 1222 preferably has a smaller band gap than the firstn-type cladding layer 121 and the first p-type cladding layer 123.Further, the first barrier layer 1222 preferably has a larger band gapthan the first well layer 1221.

[First p-Type Cladding Layer]

The first p-type cladding layer 123, which is an example of the firstp-type layer or a compound semiconductor layer, injects carriers intothe first active layer 122 and confines the carriers, together with thefirst n-type cladding layer 121. The first p-type cladding layer 123 ofthe exemplary embodiment is composed of a compound semiconductor (agroup III-V semiconductor) that lattice-matches the first well layer1221.

The first p-type cladding layer 123 preferably has the same filmthickness as the first n-type cladding layer 121. Also, the first p-typecladding layer 123 preferably has the same band gap as the first n-typecladding layer 121.

Further, the first p-type cladding layer 123 is preferably doped withp-type impurities. Containing p-type impurities at a concentration of1×10¹⁷ cm⁻³ to 5×10¹⁸ cm⁻³ is preferable in that carriers are moreeffectively injected into the first active layer 122 having a quantumwell structure, and light absorption by carries within the first p-typecladding layer 123 can be reduced. The p-type impurities may be, but notlimited to, C, Mg or Zn. The concentration of the p-type impurities inthe first p-type cladding layer 123 is preferably lower than theconcentration of the n-type impurities in the first n-type claddinglayer 121. Additionally, the first p-type cladding layer 123 preferablyhas the same composition as the first n-type cladding layer 121, exceptfor the contained impurities.

(Tunnel Junction Layer)

The tunnel junction layer 13, which is an example of the tunnel junctionpart, connects the first light-emitting layer 12 and the secondlight-emitting layer 14. By use of its own tunnel junction, the tunneljunction layer 13 passes a forward current through the firstlight-emitting layer 12 and the second light-emitting layer 14, whichare connected in series across the tunnel junction layer 13, in adirection from the second light-emitting layer 14 to the firstlight-emitting layer 12.

The tunnel junction layer 13 includes: a p-type tunnel layer 131laminated on the first p-type cladding layer 123 of the firstlight-emitting layer 12; and an n-type tunnel layer 133 on which asecond n-type cladding layer 141 (details described later) of a secondlight-emitting layer 14 is laminated. The tunnel junction layer 13further includes a highly n-type impurities-doped layer 132 between thep-type tunnel layer 131 and the n-type tunnel layer 133. Thus, thetunnel junction layer 13 of the exemplary embodiment includes the p-typetunnel layer 131 laminated on the first p-type cladding layer 123, thehighly n-type impurities-doped layer 132 laminated on the p-type tunnellayer 131, and the n-type tunnel layer 133 laminated on the highlyn-type impurities-doped layer 132.

[P-Type Tunnel Layer]

The p-type tunnel layer 131, which is an example of the third p-typelayer, forms a tunnel junction together with the n-type tunnel layer 133and the highly n-type impurities-doped layer 132. The p-type tunnellayer 131 of the exemplary embodiment is composed of a compoundsemiconductor (a group III-V semiconductor) that lattice-matches thefirst p-type cladding layer 123 and includes at least Ga (a group IIIelement) and As (a group V element). The p-type tunnel layer 131 ispreferably composed of Al_(x)Ga_(1-x)As (0≤x≤0.3). Also, the p-typetunnel layer 131 is preferably composed of a direct band gap compoundsemiconductor (group III-V semiconductor).

The p-type tunnel layer 131 preferably has a smaller film thickness thanthe first p-type cladding layer 123 of the first light-emitting layer12. Also, the p-type tunnel layer 131 preferably has a smaller band gapthan the first p-type cladding layer 123 of the first light-emittinglayer 12.

The p-type tunnel layer 131 is doped with p-type impurities. Here, thep-type tunnel layer 131 preferably contains the same p-type impuritiesas the first p-type cladding layer 123 of the first light-emitting layer12. Additionally, the concentration of the p-type impurities in thep-type tunnel layer 131 is preferably higher than the concentration ofthe p-type impurities in the first p-type cladding layer 123 of thefirst light-emitting layer 12.

[N-Type Tunnel Layer]

The n-type tunnel layer 133, which is an example of the third n-typelayer, forms a tunnel junction together with the p-type tunnel layer 131and the highly n-type impurities-doped layer 132. The n-type tunnellayer 133 of the exemplary embodiment is composed of a compoundsemiconductor (a group III-V semiconductor) that lattice-matches thep-type tunnel layer 131 and includes at least Ga, In (group IIIelements) and P (a group V element). The n-type tunnel layer 133 ispreferably composed of (Al_(x)Ga_(1-x))_(y)In_(1-y)P (0≤x≤0.2,0.4≤y≤0.6). Also, the n-type tunnel layer 133 is preferably composed ofa direct band gap compound semiconductor (group III-V semiconductor).

The n-type tunnel layer 133 preferably has a smaller film thickness thanthe p-type tunnel layer 131. Also, the n-type tunnel layer 133preferably has a larger band gap than the p-type tunnel layer 131.

The n-type tunnel layer 133 is doped with n-type impurities. Here, then-type tunnel layer 133 preferably contains the same n-type impuritiesas the first n-type cladding layer 121 of the first light-emitting layer12. Additionally, the concentration of the n-type impurities in then-type tunnel layer 133 is preferably higher than the concentration ofthe n-type impurities in the second n-type cladding layer 141 (detailsdescribed later) of the second light-emitting layer 14. Further, theconcentration of the n-type impurities in the n-type tunnel layer 133 ispreferably lower than the concentration of the p-type impurities in thep-type tunnel layer 131.

[Highly n-Type Impurities-Doped Layer]

The highly n-type impurities-doped layer 132 is located between thep-type tunnel layer 131 and the n-type tunnel layer 133 to reduceelectrical resistance of the tunnel junction layer 13. The highly n-typeimpurities-doped layer 132 of the exemplary embodiment is composed of agroup III-V semiconductor that lattice-matches each of the p-type tunnellayer 131 and the n-type tunnel layer 133. The highly n-typeimpurities-doped layer 132 may contain Ga and In as group III elementsand As and P as group V elements. Also, the highly n-typeimpurities-doped layer 132 is preferably composed of a direct band gapcompound semiconductor (group III-V semiconductor).

The highly n-type impurities-doped layer 132 preferably has a smallerfilm thickness than the p-type tunnel layer 131. Also, the highly n-typeimpurities-doped layer 132 preferably has a smaller film thickness thanthe n-type tunnel layer 133.

The highly n-type impurities-doped layer 132 is doped with n-typeimpurities. Here, the highly n-type impurities-doped layer 132preferably contains the same n-type impurities as the n-type tunnellayer 133. The concentration of the n-type impurities in the highlyn-type impurities-doped layer 132 is higher than the concentration ofthe n-type impurities in the n-type tunnel layer 133. Further, theconcentration of the n-type impurities in the highly n-typeimpurities-doped layer 132 is higher than the concentration of thep-type impurities in the p-type tunnel layer 131. In terms of reducing aforward voltage, the concentration of the n-type impurities in thehighly n-type impurities-doped layer 132 is preferably not less than1×10²⁰ cm⁻³ and not more than 1×10²¹ cm⁻³.

Although the explanation herein is given using an example where thehighly n-type impurities-doped layer 132 is present between the p-typetunnel layer 131 and the n-type tunnel layer 133, the configuration ofthe tunnel junction layer 13 is not limited to this. For example, then-type tunnel layer 133 itself may contain n-type impurities at a highconcentration (e.g. not less than 1×10²⁰ cm⁻³ and not more than 1×10²¹cm⁻³).

(Second Light-Emitting Layer)

The second light-emitting layer 14, which is an example of the secondlight-emitting part, has a so-called double hetero junction and aquantum well structure, and emits light by passing a current. In theexemplary embodiment, the second light-emitting layer 14 emits light ofthe same wavelength as that of the first light-emitting layer 12. Notethat the “same wavelength” as used in this exemplary embodiment meansthat, for example, a peak emission wavelength of the secondlight-emitting layer 14 is in the range of ±10 nm (more preferably ±5nm) of a peak emission wavelength of the first light-emitting layer 12.Therefore, emission peak wavelengths of the first light-emitting layer12 and the second light-emitting layer 14 are not required to becompletely identical to each other.

Although emission wavelengths of the first light-emitting layer 12 andthe second light-emitting layer 14 are not limited to a specificwavelength range, the emission wavelengths are preferably in the rangeof red to near-infrared regions, and more preferably in the range of anear-infrared region.

The second light-emitting layer 14 may have a different structure(material, composition, thickness, impurities concentration, etc.) fromthe first light-emitting layer 12. However, in terms of more easilyapproximating the emission wavelength of the second light-emitting layer14 to that of the first light-emitting layer 12, the secondlight-emitting layer 14 and the first light-emitting layer 12 preferablyhave a common structure. The following explanation is given using anexample where the second light-emitting layer 14 and the firstlight-emitting layer 12 have a common structure.

The second light-emitting layer 14 of the exemplary embodiment includes:a second n-type cladding layer 141 laminated on the n-type tunnel layer133; a second active layer 142 laminated on the second n-type claddinglayer 141; and a second p-type cladding layer 143 laminated on thesecond active layer 142. Further, the second active layer 142 includesplural second well layers 1421 and plural second barrier layers 1422alternately laminated on each other.

[Second n-Type Cladding Layer]

The second n-type cladding layer 141, which is an example of the secondn-type layer, injects carriers (holes and electrons) into the secondactive layer 142 and confines the carriers, together with the secondp-type cladding layer 143. The second n-type cladding layer 141 of theexemplary embodiment is composed of a compound semiconductor (a groupIII-V semiconductor) that lattice-matches the n-type tunnel layer 133 ofthe tunnel junction layer 13.

The second n-type cladding layer 141 preferably has a larger filmthickness than the n-type tunnel layer 133 of the tunnel junction layer13. Also, the second n-type cladding layer 141 preferably has a largerband gap than the n-type tunnel layer 133 of the tunnel junction layer13.

Further, the second n-type cladding layer 141 is preferably doped withn-type impurities. Containing n-type impurities at a concentration of5×10¹⁷ cm⁻³ to 1×10¹⁹ cm⁻³ is preferable in that carriers are moreeffectively injected into the second active layer 142 having a quantumwell structure, and light absorption by carries within the second n-typecladding layer 141 can be reduced. Here, the second n-type claddinglayer 141 preferably contains the same n-type impurities as the n-typetunnel layer 133 of the tunnel junction layer 13. The concentration ofthe n-type impurities in the second n-type cladding layer 141 ispreferably lower than the concentration of the n-type impurities in then-type tunnel layer 133 of the tunnel junction layer 13. Further, thesecond n-type cladding layer 141 preferably has the same composition asthe first n-type cladding layer 121. Additionally, the second n-typecladding layer 141 preferably has the same composition as the firstp-type cladding layer 123, except for the contained impurities.

[Second Active Layer]

The second active layer 142 emits light through recombination of holesand electrons. The second active layer 142 of the exemplary embodimenthas a so-called multi-quantum well (MQW) structure formed by alternatelystacking the second well layers 1421 and the second barrier layers 1422.Note that the second active layer 142 (the second well layers 1421 andthe second barrier layers 1422) basically does not contain n-typeimpurities and p-type impurities. However, during the manufacturing ofthe second active layer 142, n-type impurities and p-type impurities maybe diffused from the second n-type cladding layer 141 and the secondp-type cladding layer 143, respectively, to the second active layer 142.

{Second Well Layer}

The second well layer 1421, which is an example of the well layer, issandwiched by two adjacent second barrier layers 1422. However, in thisexample, the second well layer 1421 located lowermost in the figure (atthe side of the second n-type cladding layer 141) is sandwiched by thesecond n-type cladding layer 141 and the second barrier layer 1422.Also, in this example, the second well layer 1421 located uppermost inthe figure (at the side of the second p-type cladding layer 143) issandwiched by the second p-type cladding layer 143 and the secondbarrier layer 1422. Accordingly, in this example, the number of thesecond well layers 1421 is larger than the number of the second barrierlayers 1422 by one. The second well layer 1421 of the exemplaryembodiment is composed of a compound semiconductor (a group III-Vsemiconductor) that lattice-matches the second n-type cladding layer 141and the second p-type cladding layer 143. The second well layer 1421 ispreferably composed of (Al_(x)Ga_(1-x))_(y)In_(1-y)As_(z)P_(1-z)(0≤x≤0.2, 0.7≤y≤1.0, 0.7≤z≤1.0). Also, the second well layer 1421 ispreferably composed of a direct band gap compound semiconductor (groupIII-V semiconductor).

The second well layer 1421 preferably has a smaller film thickness thanthe second n-type cladding layer 141 and the second p-type claddinglayer 143. Additionally, the second well layer 1421 preferably has asmaller band gap than the second n-type cladding layer 141 and thesecond p-type cladding layer 143. Further, the second well layer 1421and the first well layer 1221 preferably have a common structure.

{Second Barrier Layer}

The second barrier layer 1422, which is an example of the barrier layer,sandwiches the second well layer 1421 together with an adjacent secondbarrier layer 1422. The second barrier layer 1422 of the exemplaryembodiment is composed of a compound semiconductor (a group III-Vsemiconductor) that lattice-matches the second well layer 1421. Thesecond barrier layer 1422 is preferably composed ofAl_(x)Ga_(1-x)As_(z)P_(1-z) (0≤x≤0.3, 0.7≤z≤1.0). Also, the secondbarrier layer 1422 is preferably composed of a direct band gap compoundsemiconductor (group III-V semiconductor).

The second barrier layer 1422 preferably has a smaller film thicknessthan the second n-type cladding layer 141 and the second p-type claddinglayer 143. Also, the second barrier layer 1422 preferably has a largerfilm thickness than the second well layer 1421. Additionally, the secondbarrier layer 1422 preferably has a smaller band gap than the secondn-type cladding layer 141 and the second p-type cladding layer 143.Further, the second barrier layer 1422 preferably has a larger band gapthan the second well layer 1421. The second barrier layer 1422 and thefirst barrier layer 1222 preferably have a common structure.

[Second p-Type Cladding Layer]

The second p-type cladding layer 143, which is an example of the secondp-type layer, injects carriers into the second active layer 142 andconfines the carriers, together with the second n-type cladding layer141. The second p-type cladding layer 143 of the exemplary embodiment iscomposed of a compound semiconductor (a group III-V semiconductor) thatlattice-matches the second well layer 1421.

The second p-type cladding layer 143 preferably has the same filmthickness as the second n-type cladding layer 141. Also, the secondp-type cladding layer 143 preferably has the same band gap as the secondn-type cladding layer 141.

Further, the second p-type cladding layer 143 is preferably doped withp-type impurities. Containing p-type impurities at a concentration of1×10¹⁷ cm⁻³ to 5×10¹⁸ cm⁻³ is preferable in that carriers are moreeffectively injected into the second active layer 142 having a quantumwell structure, and light absorption by carries within the second p-typecladding layer 143 can be reduced. The second p-type cladding layer 143preferably contains the same p-type impurities as the first p-typecladding layer 123. The concentration of the p-type impurities in thesecond p-type cladding layer 143 is preferably lower than theconcentration of the n-type impurities in the second n-type claddinglayer 141. Additionally, the second p-type cladding layer 143 preferablyhas the same composition as the second n-type cladding layer 141, exceptfor the contained impurities.

(P-Type Contact Layer)

The p-type contact layer 15, in which holes are carriers, is a layer forproviding a p-electrode (not shown; a positive electrode portion 20; seeFIG. 5 described later). The p-type contact layer 15 of the exemplaryembodiment is composed of a compound semiconductor (a group III-Vsemiconductor) that lattice-matches the second p-type cladding layer143.

The p-type contact layer 15 preferably has a larger film thickness thanthe second p-type cladding layer 143. Also, the p-type contact layer 15preferably has a smaller band gap than the second p-type cladding layer143.

The p-type contact layer 15 is preferably doped with p-type impurities.Containing p-type impurities at a concentration of 5×10¹⁷ cm⁻³ to 2×10¹⁹cm⁻³ is preferable in that an increase in resistance can be preventedand deterioration of crystallinity is less likely to occur. Further, thep-type contact layer 15 preferably contains the same p-type impuritiesas the second p-type cladding layer 143. Additionally, the concentrationof the p-type impurities in the p-type contact layer 15 is preferablyhigher than the concentration of the p-type impurities in the secondp-type cladding layer 143.

<Structure of the Tunnel Junction Layer>

FIG. 2 is a diagram illustrating a structure around the tunnel junctionlayer 13 shown in FIG. 1. In FIG. 2, the upper section represents thelayer structure of the tunnel junction layer 13, the middle sectionrepresents the first example of distribution of impurity concentration(dopant concentration) in the tunnel junction layer 13, and the lowersection represents the second example of distribution of impurityconcentration (dopant concentration) in the tunnel junction layer 13.

[Relationship of Thickness]

As shown in the upper section in the figure, assuming that a thicknessof the p-type tunnel layer 131 is referred to as a p-type tunnel layerthickness ta, a thickness of the highly n-type impurities-doped layer132 is referred to as an n-type highly doped layer thickness tb and athickness of the n-type tunnel layer 133 is referred to as an n-typetunnel layer thickness tc, these thicknesses preferably hold thefollowing relationship: tb<ta, tb<tc.

[Relationship of Impurity Concentration]

As shown in the upper section in the figure, in the tunnel junctionlayer 13, p-type impurities (denoted by (p) in the figure) are added tothe p-type tunnel layer 131, and n-type impurities (denoted by (n) inthe figure) are added to the highly n-type impurities-doped layer 132and the n-type tunnel layer 133. As shown in the middle and lowersections in the figure, the concentration of the n-type impurities inthe highly n-type impurities-doped layer 132 is preferably higher thanthe concentration of the n-type impurities in the n-type tunnel layer133. Also, as shown in the middle and lower sections in the figure, theconcentration of the p-type impurities (dopant concentration) in thep-type tunnel layer 131 is preferably higher than the concentration ofthe n-type impurities (dopant concentration) in the n-type tunnel layer133.

As shown in the first example in the middle section of the figure, theconcentration of the p-type impurities in the p-type tunnel layer 131may be substantially uniform in the thickness direction, and theconcentration of the n-type impurities in the n-type tunnel layer 133may be substantially uniform in the thickness direction. Alternatively,as shown in the second example in the lower section of the figure, theconcentration of the p-type impurities in the p-type tunnel layer 131may be higher at the boundary with the highly n-type impurities-dopedlayer 132 than at the boundary with the first p-type cladding layer 123,and the concentration of the n-type impurities in the n-type tunnellayer 133 may be higher at the boundary with the highly n-typeimpurities-doped layer 132 than at the boundary with the second n-typecladding layer 141.

Although the second example in the lower section of the figure indicatesthat the concentration of the p-type impurities in the p-type tunnellayer 131 and the concentration of the n-type impurities in the n-typetunnel layer 133 change linearly in the thickness direction, theconcentration may change in a different manner. For example, theconcentration may change curvedly or stepwise.

<Method for Manufacturing the Semiconductor Layer Forming Substrate>

FIG. 3 is a flowchart illustrating a method for manufacturing thesemiconductor layer forming substrate 1 as shown in FIG. 1. Note thatthe semiconductor layer forming substrate 1 of the exemplary embodimentis obtained by forming the light-emitting element layer 10 on the growthsubstrate 1 a using a metal organic chemical vapor deposition (MOCVD)method. However, the method for manufacturing the semiconductor layerforming substrate 1 is not limited to this; for example, a molecularbeam epitaxy (MBE) method may be used.

[N-Type Contact Layer Forming Process]

First, material gases of elements constituting the n-type contact layer11 (a group III element, a group V element, and an element constitutingthe n-type impurities) as well as a carrier gas are supplied into achamber accommodating the growth substrate 1 a (step 10). In step 10,the n-type contact layer 11 is laminated on the growth substrate 1 a.

[First n-Type Cladding Layer Forming Process]

Then, with the carrier gas being continuously supplied, material gasesof elements constituting the first n-type cladding layer 121 (a groupIII element, a group V element, and an element constituting the n-typeimpurities) are supplied into the chamber accommodating the growthsubstrate 1 a, on which the n-type contact layer 11 has been laminated(step 20). In step 20, the first n-type cladding layer 121 is laminatedon the n-type contact layer 11.

[First Active Layer Forming Process]

Then, with the carrier gas being continuously supplied, material gasesof elements constituting the first well layers 1221 (a group III elementand a group V element) and material gases of elements constituting thefirst barrier layers 1222 (a group III element and a group V element)are alternately supplied into the chamber accommodating the growthsubstrate 1 a, on which the layers up to the first n-type cladding layer121 have been laminated (step 30). In step 30, the first active layer122 composed of the alternately laminated first well layers 1221 andfirst barrier layers 1222 is formed on the first n-type cladding layer121.

[First p-Type Cladding Layer Forming Process]

With the carrier gas being continuously supplied, material gases ofelements constituting the first p-type cladding layer 123 (a group IIIelement, a group V element, and an element constituting the p-typeimpurities) are supplied into the chamber accommodating the growthsubstrate 1 a, on which the layers up to the first active layer 122 havebeen laminated (step 40). In step 40, the first p-type cladding layer123 is laminated on the first active layer 122.

Through the above processes, the first light-emitting layer 12 is formedon the n-type contact layer 11.

[P-Type Tunnel Layer Forming Process]

Then, with the carrier gas being continuously supplied, material gasesof elements constituting the p-type tunnel layer 131 (a group IIIelement, a group V element, and an element constituting the p-typeimpurities) are supplied into the chamber accommodating the growthsubstrate 1 a, on which the layers up to the first p-type cladding layer123 have been laminated (step 50). In step 50, the p-type tunnel layer131 is laminated on the first p-type cladding layer 123.

[N-Type Tunnel Layer Forming Process]

Then, with the carrier gas being continuously supplied, material gasesof elements constituting the n-type tunnel layer 133 (a group IIIelement, a group V element, and an element constituting the n-typeimpurities) are supplied into the chamber accommodating the growthsubstrate 1 a, on which the layers up to the p-type tunnel layer 131have been laminated (step 60). In step 60, the n-type tunnel layer 133is laminated on the p-type tunnel layer 131.

Here, when the processing goes from step 50 to step 60, the exemplaryembodiment uses a devised method for supplying the material gases intothe chamber. This method enables to form, between the p-type tunnellayer 131 and the n-type tunnel layer 133, the highly n-typeimpurities-doped layer 132 having a higher concentration of n-typeimpurities than the n-type tunnel layer 133. Details of the method willbe described in later.

Through the above processes, the tunnel junction layer 13 is formed onthe first light-emitting layer 12.

[Second n-Type Cladding Layer Forming Process]

Then, with the carrier gas being continuously supplied, material gasesof elements constituting the second n-type cladding layer 141 (a groupIII element, a group V element, and an element constituting the n-typeimpurities) are supplied into the chamber accommodating the growthsubstrate 1 a, on which the layers up to the n-type tunnel layer 133have been laminated (step 70). In step 70, the second n-type claddinglayer 141 is laminated on the n-type tunnel layer 133.

[Second Active Layer Forming Process]

Subsequently, with the carrier gas being continuously supplied, materialgases of elements constituting the second well layers 1421 (a group IIIelement and a group V element) and material gases of elementsconstituting the second barrier layers 1422 (a group III element and agroup V element) are alternately supplied into the chamber accommodatingthe growth substrate 1 a, on which the layers up to the second n-typecladding layer 141 have been laminated (step 80). In step 80, the secondactive layer 142 composed of the alternately laminated second welllayers 1421 and second barrier layers 1422 is formed on the secondn-type cladding layer 141.

[Second p-Type Cladding Layer Forming Process]

Then, with the carrier gas being continuously supplied, material gasesof elements constituting the second p-type cladding layer 143 (a groupIII element, a group V element, and an element constituting the p-typeimpurities) are supplied into the chamber accommodating the growthsubstrate 1 a, on which the layers up to the second active layer 142have been laminated (step 90). In step 90, the second p-type claddinglayer 143 is laminated on the second active layer 142.

Through the above processes, the second light-emitting layer 14 isformed on the tunnel junction layer 13.

[P-Type Contact Layer Forming Process]

Finally, with the carrier gas being continuously supplied, materialgases of elements constituting the p-type contact layer 15 (a group IIIelement, a group V element, and an element constituting the p-typeimpurities) are supplied into the chamber accommodating the growthsubstrate 1 a, on which the layers up to the second p-type claddinglayer 143 have been laminated (step 100). In step 100, the p-typecontact layer 15 is laminated on the second p-type cladding layer 143.

Through the above processes, the semiconductor layer forming substrate 1is obtained that consists of the n-type contact layer 11, the firstlight-emitting layer 12, the tunnel junction layer 13, the secondlight-emitting layer 14 and the p-type contact layer 15 laminated inthis order on the growth substrate 1 a.

<Method for Manufacturing the Tunnel Junction Layer>

Now, the method for manufacturing the tunnel junction layer 13, which isa part of the aforementioned method for manufacturing the semiconductorlayer forming substrate 1, will be described in more detail.

FIG. 4 is a timing chart illustrating the method for manufacturing thetunnel junction layer 13. In FIG. 4, the horizontal axis representselapse of time (referred to as “growth time” in the figure). Also, FIG.4 shows the relationship between three processes (the first to the thirdprocesses) performed in manufacturing the tunnel junction layer 13 andmaterial gases supplied into the chamber in the respective processes.Here, the first process corresponds to step 50 in FIG. 3 and the thirdprocess corresponds to step 60 in FIG. 3.

Note that the explanation herein is given using an example where thep-type tunnel layer 131 is composed of AlGaAs, the highly n-typeimpurities-doped layer 132 and the n-type tunnel layer 133 are composedof GaInP, the p-type impurities are C, and the n-type impurities are Te.

As described above, the tunnel junction layer 13 of the exemplaryembodiment is formed by the MOCVD method. Note that the explanation isgiven assuming that hydrogen (H₂) is a carrier gas, tetrabromomethane(CBr₄) is a C material gas, trimethylgallium (TMG) is a Ga material gas,trimethylaluminium (TMAl) is an Al material gas, arsine (AsH₃) is an Asmaterial gas, diethyltellurium (DETe) is a Te material gas,trimethylindium (TMIn) is an In material gas, and phosphine (PH₃) is a Pmaterial gas.

[Pre-Processes Before the First Process]

In the pre-processes before the first process, namely in steps 10 to 40shown in FIG. 3, a temperature (a substrate temperature) of the growthsubstrate 1 a inside the chamber is set to the first growth temperature(e.g. about 650° C.). At the start of the first process after finishingthe pre-processes (specifically step 40), the substrate temperature isset to the second growth temperature that is lower than the first growthtemperature by 100° C. to 150° C. (e.g. 500° C.). Note that thesubstrate temperature is maintained at the second growth temperaturethroughout the first to the third processes.

[First Process]

In the first process, the carrier gas and the various material gases forthe p-type tunnel layer 131 are supplied into the chamber. The materialgases are the C material gas (including an element constituting thep-type impurities; corresponds to the third material gas), the Gamaterial gas (including a group III element; corresponds to the firstmaterial gas), the Al material gas (including a group III element;corresponds to the first material gas), and the As material gas(including a group V element; corresponds to the second material gas).

The first process is performed during the first period T1 that runs fromthe first process start time t0 to the first process end time t1.

[Second Process]

In the second process subsequent to the first process, supply of thevarious material gases for the p-type tunnel layer 131, which have beensupplied in the first process, is stopped, and the carrier gas and theTe material gas (including an element constituting the n-typeimpurities; corresponds to the fourth material gas) are supplied intothe chamber.

The second process is performed during the second period T2 that runsfrom the first process end time (the second process start time) t1 tothe second process end time t2. In the exemplary embodiment, the secondperiod T2 is preferably shorter than the first period T1.

[Third Process]

In the third process subsequent to the second process, the carrier gasand the various material gases for the highly n-type impurities-dopedlayer 132 and the n-type tunnel layer 133 are supplied into the chamber.The material gases are the Te material gas (including an elementconstituting the n-type impurities; corresponds to the fourth materialgas), the Ga material gas (including a group III element; corresponds tothe fifth material gas), the In material gas (including a group IIIelement; corresponds to the fifth material gas), and the P material gas(including a group V element; corresponds to the sixth material gas).

The third process is performed during the third period T3 that runs fromthe second process end time (the third process start time) t2 to thethird process end time t3. In the exemplary embodiment, the third periodT3 is preferably longer than the second period T2.

[Post-Processes after the Third Process]

In the post-processes after the third process, namely in steps 70 to 100shown in FIG. 3, the temperature (the substrate temperature) of thegrowth substrate 1 a inside the chamber is set to the first growthtemperature (e.g. about 650° C.). Accordingly, at the start of step 70after finishing the third process (specifically step 60), the substratetemperature is reset to the first growth temperature (e.g. about 650°C.) that is higher than the second growth temperature by 100° C. to 150°C.

In the first to the third processes, the growth temperature is madelower than that in the pre- and post-processes (the pre-processes beforethe first process and the post-processes after the third process). Thisis done to dope the tunnel junction layer 13 with a larger amount ofimpurities (p-type impurities or n-type impurities) than the otherlayers.

<Structure of the Semiconductor Light-Emitting Element>

FIG. 5 is a diagram illustrating a cross-sectional structure of asemiconductor light-emitting element 2 including the light-emittingelement layer 10. As shown in the FIG. 5, the semiconductorlight-emitting element 2 includes the light-emitting element layer 10,but does not include the growth substrate 1 a, which constitutes thesemiconductor layer forming substrate 1 together with the light-emittingelement layer 10.

The semiconductor light-emitting element 2 includes: the aforementionedlight-emitting element layer 10; the positive electrode portion 20connected to the p-type contact layer 15 of the light-emitting elementlayer 10; and the negative electrode portion 30 connected to the n-typecontact layer 11 of the light-emitting element layer 10. The positiveelectrode portion 20 functions as a p-electrode of the firstlight-emitting layer 12 and the second light-emitting layer 14 of thelight-emitting element layer 10. On the other hand, the negativeelectrode portion 30 functions as an n-electrode of the firstlight-emitting layer 12 and the second light-emitting layer 14 of thelight-emitting element layer 10. The positive electrode portion 20further functions as a reflection film by which light emitted from thefirst light-emitting layer 12 and the second light-emitting layer 14 tothe positive electrode portion 20 side is reflected toward the negativeelectrode portion 30 side. The positive electrode portion 20 is formedon the almost entire surface of the lower side (in the figure) of eachsemiconductor light-emitting element 2. On the other hand, the nativeelectrode portion 30 is formed in an island shape on a part of the upperside (in the figure) of each semiconductor light-emitting element 2.

[Positive Electrode Portion]

The positive electrode portion 20 includes: a p-electrode layer 21laminated on the p-type contact layer 15 of the light-emitting elementlayer 10; a reflection layer 22 laminated on the p-electrode layer 21;and a diffusion preventing layer 23 laminated on the reflection layer22. The positive electrode portion 20 further includes: a joining layer24 laminated on the diffusion preventing layer 23; an internal electrodelayer 25 laminated on the joining layer 24; a support substrate 26laminated on the internal electrode layer 25; and an external electrodelayer 27 laminated on the support substrate 26 and exposed to theoutside.

(P-Electrode Layer)

The p-electrode layer 21 is for supplying a current to the firstlight-emitting layer 12 and the second light-emitting layer 14 of thelight-emitting element layer 10 by diffusing it in a surface direction.The p-electrode layer 21 includes: a light-transmitting layer 211 withplural through holes penetrating in the thickness direction; and pluralcolumnar electrode layers 212 filling the respective through-holes.

[Light-Transmitting Layer]

The light-transmitting layer 211 has insulation properties and transmitslight emitted from the first light-emitting layer 12 and the secondlight-emitting layer 14 of the light-emitting element layer 10. Thelight-transmitting layer 211 may be made of SiO₂ or the like.

[Columnar Electrode Layer]

The columnar electrode layer 212 has conductivity and makes ohmiccontact with the p-type contact layer 15 of the light-emitting elementlayer 10. The columnar electrode layer 212 may be made of AuBe or thelike.

(Reflection Layer)

The reflection layer 22 has conductivity and reflects light emitted fromthe first light-emitting layer 12 and the second light-emitting layer 14of the light-emitting element layer 10. The reflection layer 22 may bemade of an AgPdCu (APC) alloy, a metal such as Au, Cu, Ag, Al or Pt, oran alloy of these metals or the like.

(Diffusion Preventing Layer)

The diffusion preventing layer 23 has conductivity and prevents metalscontained in the joining layer 24, the support substrate 26 and the likefrom diffusing to the reflection layer 22 side and reacting with thereflection layer 22. The diffusion preventing layer 23 may be made of ametal such as Ni, Ti, Pt, Cr, Ta, W or Mo. Alternatively, the diffusionpreventing layer 23 may be formed by laminating plural metal layers ofmetals selected from the above metals.

(Joining Layer)

The joining layer 24 has conductivity and joins the diffusion preventinglayer 23 formed above the light-emitting element layer 10 and theinternal electrode layer 25 formed on the support substrate 26. Thejoining layer 24 may be made of an Au-based eutectic metal or the like,which is chemically stable and has a low melting point. Examples of theAu-based eutectic metal include AuGe, AuSn, AuSi and AuIn.

(Internal Electrode Layer)

The internal electrode layer 25 has conductivity and electricallyconnects the joining layer 24 and the support substrate 26. The internalelectrode layer 25 may be made of a metal material of various kinds, ormay be formed by laminating plural metal layers.

(Support Substrate)

The support substrate 26 has conductivity and physically supports thelight-emitting element layer 10, which is obtained by removing thegrowth substrate 1 a from the semiconductor layer forming substrate 1.In this example, the reflection layer 22 is arranged between thelight-emitting element layer 10 (the first light-emitting layer 12 andthe second light-emitting layer 14) and the support substrate 26. Forthis reason, the support substrate 26 may be made of a material thatabsorbs light emitted from the first light-emitting layer 12 and thesecond light-emitting layer 14. The support substrate 26 may be a Gewafer, an Si wafer, a GaAs wafer, a GaP wafer or the like.

(External Electrode Layer)

The external electrode layer 27 has conductivity and is electricallyconnected to the wiring (not shown) provided outside. The externalelectrode layer 27 may be made of a metal material of various kinds, ormay be formed by laminating plural metal layers.

[Negative Electrode Portion]

The negative electrode portion 30 may be made of a metal of variouskinds, or may be formed by laminating plural metal layers.

<Method for Manufacturing the Semiconductor Light-Emitting Element>

Now, the method for manufacturing the semiconductor light-emittingelement 2 shown in FIG. 5 will be described using a specific example.

FIG. 6 is a flowchart illustrating the method for manufacturing thesemiconductor light-emitting element 2.

[Positive Electrode Portion Forming Process]

First, the positive electrode portion 20 is formed on the p-type contactlayer 15 of the semiconductor layer forming substrate 1 including thegrowth substrate 1 a and the light-emitting element layer 10 (step 110).The positive electrode portion forming process of step 110 includesplural processes (steps 111 to 117 in this example) explained below.

(P-Electrode Layer Forming Process)

In the positive electrode portion forming process of step 110, first,the p-electrode layer 21 is formed on the p-type contact layer 15 of thelight-emitting element layer 10 (step 111). Note that, in thep-electrode layer forming process of step 111, the light-transmittinglayer 211 is formed first (step 111 a), and then the columnar electrodelayers 212 are formed (step 111 b).

[Light-Transmitting Layer Forming Process]

In the light-transmitting layer forming process of step 111 a, SiO₂ isdeposited on the entire surface of the p-type contact layer 15 bychemical vapor deposition (CVD), and the SiO₂ is then etched to makeplural through holes in the positions in which the respective columnarelectrode layers 212 are to be formed. At this time, the thickness ofthe SiO₂ is set at approximately 0.3 μm. The light-transmitting layer211 made of SiO₂ is thus obtained.

[Columnar Electrode Layer Forming Process]

In the columnar electrode layer forming process of step 111 b, AuBe isfilled into each of the through holes in the light-transmitting layer211 by vapor deposition to form plural columnar electrode layers 212.The thickness of the AuBe is made equal to the thickness of thelight-transmitting layer 211. The p-electrode layer 21 including thelight-transmitting layer 211 and the plural columnar electrode layers212 is thus obtained.

(Reflection Layer Forming Process)

Then, Au is deposited on the p-electrode layer 21 by vapor deposition toform the reflection layer 22 (step 112). The thickness of the reflectionlayer 22 is set at approximately 0.7 μm.

(Diffusion Preventing Layer Forming Process)

Subsequently, Pt and Ti are deposited in this order on the reflectionlayer 22 by vapor deposition to form the diffusion preventing layer 23with a lamination structure of a Pt layer and a Ti layer (step 113). Thethickness of the diffusion preventing layer 23 is set at approximately0.5 μm.

(Joining Layer Forming Process)

Then, AuGe is deposited on the diffusion preventing layer 23 by vapordeposition to form the joining layer 24 (step 114). The thickness of thejoining layer 24 is set at approximately 1.0 μm. At this moment, thep-electrode layer 21, the reflection layer 22, the diffusion preventinglayer 23 and the joining layer 24 are laminated on the p-type contactlayer 15 of the light-emitting element layer 10 of the semiconductorlayer forming substrate 1 including the growth substrate 1 a.Hereinafter, the structure formed by laminating the p-electrode layer21, the reflection layer 22, the diffusion preventing layer 23 and thejoining layer 24 on the semiconductor layer forming substrate 1 isreferred to as the “first laminated body”.

(Internal Electrode Layer Forming Process)

Besides the above first laminated body, the support substrate 26 made ofa Ge wafer is prepared. Pt and Au are deposited in this order on onesurface (front surface) of the support substrate 26 by vapor depositionto form the internal electrode layer 25 with a lamination structure of aPt layer and an Au layer (step 115). The thicknesses of the Pt layer andthe Au layer of the internal electrode layer 25 are set at approximately0.1 μm and approximately 0.5 μm, respectively.

(External Electrode Layer Forming Process)

Then, Pt and Au are deposited in this order on the other surface (rearsurface) of the support substrate 26 by vapor deposition to form theexternal electrode layer 27 with a lamination structure of a Pt layerand an Au layer (step 116). The thicknesses of the Pt layer and the Aulayer of the external electrode layer 27 are set at approximately 0.1 μmand approximately 0.5 μm, respectively. At this moment, the internalelectrode layer 25 and the external electrode layer 27 are laminated onthe front surface and the rear surface of the support substrate 26,respectively. Hereinafter, the structure formed by laminating theinternal electrode layer 25 and the external electrode layer 27 on thesupport substrate 26 is referred to as the “second laminated body”.

(Joining Process)

The joining layer 24 of the first laminated body and the internalelectrode layer 25 of the second laminated body are brought intoface-to-face contact with each other. In this state, the first laminatedbody and the second laminated body are heated and pressurized to bejoined with each other (step 117). The heating temperature is set atapproximately 400° C. and the applied pressure is set at approximately500 kgf. At this moment, the semiconductor layer forming substrate 1including the growth substrate 1 a and the light-emitting element layer10, and the positive electrode portion 20 are laminated. Hereinafter,the structure formed by laminating the semiconductor layer formingsubstrate 1 and the positive electrode portion 20 is referred to as the“third laminated body”.

Thus, the positive electrode portion forming process of step 110 isfinished.

[Growth Substrate Removing Process]

Subsequently, the third laminated body is wet-etched to separate thegrowth substrate 1 a and the light-emitting element layer 10 of thesemiconductor layer forming substrate 1, removing the growth substrate 1a from the third laminated body (step 120). At this moment, thelight-emitting element layer 10 and the positive electrode portion 20are laminated with the n-type contact layer 11 of the light-emittingelement layer 10 being exposed to the outside. Hereinafter, thestructure formed by laminating the light-emitting element layer 10 andthe positive electrode portion 20 is referred to as the “fourthlaminated body”.

[Negative Electrode Portion Forming Process]

Next, plural negative electrode portions 30 are formed on the n-typecontact layer 11 of the light-emitting element layer 10 in the fourthlaminated body (step 130). In this example, an AuGe—Ni alloy, Ti and Auare deposited in this order on the n-type contact layer 11. This formsthe negative electrode portion 30 composed of an AuGe—Ni alloy layer, aTi layer and an Au layer laminated in this order. The thicknesses of theAuGe—Ni alloy layer, the Ti layer and the Au layer of the negativeelectrode portion 30 are set at approximately 0.5 μm, approximately 0.2μm and approximately 1.0 μm, respectively. At this moment, the pluralnegative electrode portions 30 are arranged in a matrix on the surfaceof the n-type contact layer 11 of the light-emitting element layer 10,which is one of the surfaces of the fourth laminated body consisting ofthe light-emitting element layer 10 and the positive electrode portion20. Hereinafter, the structure formed by laminating the positiveelectrode portion 20 and the plural negative electrode portions 30 onthe light-emitting element layer 10 is referred to as the “fifthlaminated body”.

[Dividing Process]

Finally, the fifth laminated body is wet-etched and irradiated withlaser, so that the fifth laminated body is divided into pluralsemiconductor light-emitting elements 2 (step 140). The dividing processof step 140 is performed such that each individual light-emittingelement 2 includes one negative electrode portion 30.

Through the above processes, the semiconductor light-emitting elements 2each including the light-emitting element layer 10, the positiveelectrode portion 20 and the negative electrode portion 30 are obtained.

<Light Emission Operation of the Semiconductor Light-Emitting Element>

Now, light emission operation of the semiconductor light-emittingelement 2 thus obtained will be explained.

In response to a forward voltage being applied to the positive electrodeportion 20 and the negative electrode portion 30 of the semiconductorlight-emitting element 2, a current (a forward current) passes throughthe light-emitting element layer 10 in a direction from the p-typecontact layer 15 to the n-type contact layer 11. In the exemplaryembodiment, the first light-emitting layer 12 and the secondlight-emitting layer 14 are connected via the tunnel junction layer 13,which makes the flow of the forward current less interrupted.

In response to the forward current passing through the firstlight-emitting layer 12 and the second light-emitting layer 14, thefirst light-emitting layer 12 and the second light-emitting layer 14each emit light of the same wavelength. The light emitted from the firstlight-emitting layer 12 is mostly directed toward the n-type contactlayer 11 side (the upper side in FIG. 5) and the tunnel junction layer13 side (the lower side in FIG. 5). On the other hand, the light emittedfrom the second light-emitting layer 14 is mostly directed toward thetunnel junction layer 13 side (the upper side in FIG. 5) and the p-typecontact layer 15 side (the lower side in FIG. 5).

Here, the light emitted from the first light-emitting layer 12 and thesecond light-emitting layer 14 toward the upper side in FIG. 5 isoutputted to the outside via the n-type contact layer 11 (refer to anarrow in the figure). On the other hand, the light emitted from thefirst light-emitting layer 12 and the second light-emitting layer 14toward the lower side in FIG. 5 is reflected by the reflection layer 22and goes toward the n-type contact layer 11 side (the upper side in FIG.5).

Meanwhile, the light emitted from the first light-emitting layer 12 andthe second light-emitting layer 14 passes through the tunnel junctionlayer 13 in the light-emitting element layer 10. Here, in the exemplaryembodiment, the n-type tunnel layer 133 of the tunnel junction layer 13is composed of a group III-V semiconductor containing P (a phosphide).This enables to make the band gap of the n-type tunnel layer 133 largerthan one that is composed of a group III-V semiconductor containing As(an arsenide). As a result, the light emitted from the firstlight-emitting layer 12 and the second light-emitting layer 14 is lessabsorbed by the n-type tunnel layer 133, which can increase the emissionoutput of the light-emitting element layer 10, and ultimately thesemiconductor light-emitting element 2.

Further, in the exemplary embodiment, the highly n-type impurities-dopedlayer 132 is arranged at the boundary between the p-type tunnel layer131 and the n-type tunnel layer 133 of the tunnel junction layer 13.This lowers the resistance of the tunnel junction layer 13 in accordancewith an increase in carriers, allowing for preventing an increase in theforward voltage in the semiconductor light-emitting element 2.

Further, in the exemplary embodiment, the light-emitting element layer10 is manufactured at the growth temperature of 650° C. to 700° C. forthe first light-emitting layer 12 and the second light-emitting layer14, and at the growth temperature lower than the above temperature by100° C. to 150° C. for the tunnel junction layer 13. For example, in acase where GaInP is formed using a MOCVD method, the PL peak energy(nearly equal to the band gap) of GaInP becomes minimum at the growthtemperature of 650° C., and becomes larger above or below 650° C. Forthis reason, if the tunnel junction layer 13 is formed at the growthtemperature below 650° C., transparency of the tunnel junction layer 13to the light emitted from the first light-emitting layer 12 and thesecond light-emitting layer 14 is expected to increase.

<Others>

Although the exemplary embodiment has been explained using the examplewhere the two light-emitting layers (the first light-emitting layer 12and the second light-emitting layer 14) are connected via the singletunnel junction layer 13, the present invention is not limited to thisstructure. For example, more than two light-emitting layers and morethan one tunnel junction layer 13 may be alternately connected.

Although in the exemplary embodiment the first active layer 122 of thefirst light-emitting layer 12 and the second active layer 142 of thesecond light-emitting layer 14 each have a so-called multi-quantum wellstructure, the present invention is not limited to this structure. Forexample, these active layers may have a so-called single quantum wellstructure, or may have a simple double heterojunction structure.

Although the exemplary embodiment has been explained using the examplewhere the semiconductor light-emitting element 2 including thelight-emitting element layer 10 is provided with the reflection layer22, the structure of the semiconductor light-emitting element 2 may bechanged as appropriate.

Although in the exemplary embodiment the highly n-type impurities-dopedlayer 132 is arranged between the p-type tunnel layer 131 and the n-typetunnel layer 133 of the tunnel junction layer 13, the highly n-typeimpurities-doped layer 132 is not essential. That is, the tunneljunction layer 13 may be composed of the p-type tunnel layer 131 and then-type tunnel layer 133 directly laminated on each other.

EXAMPLES

Hereinafter, the present invention will be described in more detailbased on the Examples. However, it should be noted that the presentinvention is not limited to the Examples below as long as the gist ofthe present invention is maintained.

The inventors manufactured semiconductor layer forming substrates 1 eachhaving a tunnel junction layer 13 of a different composition. Theinventors then evaluated various properties of semiconductorlight-emitting elements 2 obtained from the respective semiconductorlayer forming substrates 1.

Table 1 shows conditions for manufacturing the semiconductor layerforming substrate 1 of the Example 1. Table 2 shows relationship betweenthe tunnel junction layers of the semiconductor layer forming substrates1 of the Examples 1 to 3 and the Comparative Example.

TABLE 1 [EXAMPLE 1] EMISSION WAVELENGTH 810 nm CONCEN- DOP- TRATIONTHICKNESS LAYER STRUCTURE MATERIAL ANT (/cm³) (μm) LIGHT P-TYPE CONTACTLAYER 15 AlGaAs C 3.0E+18 3.50 EMITTING SECOND LIGHT SECOND P-TYPECLADDING LAYER 143 AlGaAs C 8.0E+17 0.20 ELEMENT EMITTING SECOND ACTIVESECOND BARRIER AlGaAsP UN — 0.119(0.007 × 17) LAYER 10 LAYER 14 LAVER142 LAYER 1422 SECOND WELL LAYER 1421 AlGaInAsP UN — 0.0594(0.0033 × 18)SECOND N-TYPE CLADDING LAYER 141 Al0.45Ga0.55As Te 1.0E+18 0.20 TUNNELJUNCTION N-TYPE TUNNEL LAYER 133 Ga0.51In0.49P Te 2.5E+19  0.015 LAYER13 P-TYPE TUNNEL LAYER 131 Al0.25Ga0.75As C 4.0E+19  0.020 FIRST LIGHTFIRST P-TYPE CLADDING LAYER 123 Al0.45Ga0.55As C 8.0E+17 0.20 EMITTINGFIRST ACTIVE FIRST BARRIER AlGaAsP UN — 0.119(0.007 × 17) LAYER 12 LAYER122 LAYER 1222 FIRST WELL LAYER 1221 AlGaInAsP UN — 0.0594(0.0033 × 18)FIRST N-TYPE CLADDING LAYER 121 AlGaAs Te 1.0E+18 0.20 N-TYPE CONTACTLAYER 11 AlGaAs Te 5.0E+17 5.00 GROWTH SURSTRAT 1a GaAs Si 1.0E+18350   

TABLE 2 MATERIAL OF MATERIAL OF HIGHLY N-TYPE IMPURITY CONCENTRATION INP-TYPE TUNNEL N-TYPE TUNNEL IMPURITIES-DOPED P-TYPE TUNNEL LAYER 131 &LAYER 131 LAYER 133 LAYER 132 N-TYPE TUNNEL LAYER 133 EXAMPLE 1 AlGaAsGaInP YES CONSTANT EXAMPLE 2 AlGaAs GaInP YES INCLINED EXAMPLE 3 AlGaAsGaInP NO CONSTANT COMPARATIVE AlGaAs AlGaAs YES CONSTANT EXAMPLE<Semiconductor Layer Forming Substrate of the Example 1>

Now, the semiconductor layer forming substrate 1 of the Example 1 willbe explained with reference to Table 1.

[Growth Substrate]

As the growth substrate 1 a, a wafer of GaAs single crystal added withan Si dopant, which is an n-type impurity, was used. Carrierconcentration in the wafer was 1.0×10¹⁸ (/cm³) (described as “1.0E+18”in Table 1; the same applies hereafter). Here, carrier concentration inthe growth substrate 1 a is preferably selected from a range of 5.0×10¹⁷(/cm³) to 2.0×10¹⁸ (/cm³). The thickness of the growth substrate 1 a wasset to 350 (μm), and the off-angle of the crystal growth plane on thegrowth substrate 1 a was set to 15°.

[Light-Emitting Element Layer]

The light-emitting element layer 10 was configured as follows. Emissionwavelength (as a design value) of the light-emitting element layer 10(more specifically the first light-emitting layer 12 and the secondlight-emitting layer 14) was set to 810 nm.

(N-Type Contact Layer)

As the n-type contact layer 11, AlGaAs was used. The n-type contactlayer 11 was added with a Te dopant, which is an n-type impurity, at aconcentration of 5.0×10¹⁷ (/cm³). The thickness of the n-type contactlayer 11 was set to 5.00 (μm).

(First Light-Emitting Layer)

The first light-emitting layer 12 was configured as follows.

[First n-Type Cladding Layer]

As the first n-type cladding layer 121, AlGaAs was used. The firstn-type cladding layer 121 was added with a Te dopant, which is an n-typeimpurity, at a concentration of 1.0×10¹⁸ (/cm³). The thickness of thefirst n-type cladding layer 121 was set to 0.20 (μm).

[First Active Layer]

The first active layer 122 was configured as follows. Note that eighteenfirst well layers 1221 and seventeen first barrier layers 1222 wereformed.

{First Well Layer}

As the first well layers 1221, AlGaInAsP was used. The first well layers1221 were not added with a dopant (i.e. they were undoped; described as“UN” in Table 1; the same applies hereafter). The thickness of one firstwell layer 1221 was set to 0.0033 (μm). Accordingly, the total thicknessof all (eighteen) first well layers 1221 was 0.0594 (μm).

{First Barrier Layer}

As the first barrier layers 1222, AlGaAsP was used. The first barrierlayers 1222 were not added with a dopant (i.e. they were undoped). Thethickness of one first barrier layer 1222 was set to 0.007 (μm).Accordingly, the total thickness of all (seventeen) first barrier layers1222 was 0.119 (μm).

[First p-Type Cladding Layer]

As the first p-type cladding layer 123, Al_(0.45)Ga_(0.55)As (describedas “Al0.45Ga0.55As” in Table 1; the same applies hereafter) was used.The first p-type cladding layer 123 was added with a C dopant, which isa p-type impurity, at a concentration of 8.0×10¹⁷ (/cm³). The thicknessof the first p-type cladding layer 123 was set to 0.20 (μm).

(Tunnel Junction Layer)

The tunnel junction layer 13 was configured as follows.

[P-Type Tunnel Layer]

As the p-type tunnel layer 131, Al_(0.25)Ga_(0.75)As was used. Thep-type tunnel layer 131 was added with a C dopant, which is a p-typeimpurity, at a concentration of 4.0×10¹⁹ (/cm³). The thickness of thep-type tunnel layer 131 was set to 0.020 (μm).

[N-Type Tunnel Layer]

As the n-type tunnel layer 133, Ga_(0.51)In_(0.49)P was used. The n-typetunnel layer 133 was added with a Te dopant, which is an n-typeimpurity, at a concentration of 2.5×10¹⁹ (/cm³). The thickness of then-type tunnel layer 133 was set to 0.015 (μm).

[Highly n-Type Impurities-Doped Layer]

In the Example 1, the tunnel junction layer 13 was manufacturedaccording to the procedure shown in FIG. 4. Thus, the highly n-typeimpurities-doped layer 132 having a larger amount of Te as n-typeimpurities than the n-type tunnel layer 133 is present between thep-type tunnel layer 131 and the n-type tunnel layer 133 (detailsdescribed later), although not shown in Table 1.

(Second Light-Emitting Layer)

The second light-emitting layer 14 was configured as follows. Note thateach layer in the second light-emitting layer 14 was configured to havea structure that is common to each corresponding layer in the firstlight-emitting layer 12.

[Second n-Type Cladding Layer]

As the second n-type cladding layer 141, Al_(0.45)Ga_(0.55)As was used.The second n-type cladding layer 141 was added with a Te dopant, whichis an n-type impurity, at a concentration of 1.0×10¹⁸ (/cm³). Thethickness of the second n-type cladding layer 141 was set to 0.20 (μm).

[Second Active Layer]

The second active layer 142 was configured as follows. Note thateighteen second well layers 1421 and seventeen second barrier layers1422 were formed.

{Second Well Layer}

As the second well layers 1421, AlGaInAsP was used. The second welllayers 1421 were not added with a dopant (i.e. they were undoped). Thethickness of one second well layer 1421 was set to 0.0033 (μm).Accordingly, the total thickness of all (eighteen) second well layers1421 was 0.0594 (μm).

{Second Barrier Layer}

As the second barrier layers 1422, AlGaAsP was used. The second barrierlayers 1422 were not added with a dopant (i.e. they were undoped). Thethickness of one second barrier layer 1422 was set to 0.007 (μm).Accordingly, the total thickness of all (seventeen) second barrierlayers 1422 was 0.119 (μm).

[Second p-Type Cladding Layer]

As the second p-type cladding layer 143, AlGaAs was used. The secondp-type cladding layer 143 was added with a C dopant, which is a p-typeimpurity, at a concentration of 8.0×10¹⁷ (/cm³). The thickness of thesecond p-type cladding layer 143 was set to 0.20 (μm).

(P-Type Contact Layer)

As the p-type contact layer 15, AlGaAs was used. The p-type contactlayer 15 was added with a C dopant, which is a p-type impurity, at aconcentration of 3.0×10¹⁸ (/cm³). The thickness of the p-type contactlayer 15 was 3.50 (μm).

<Relationship Between the Semiconductor Layer Forming Substrates of theExamples and the Comparative Example>

Next, with reference to Table 2, relationship between the tunneljunction layers 13 of the semiconductor layer forming substrates 1 ofthe Examples (the Examples 1 to 3) and the Comparative Example will beexplained. Table 2 shows materials of the p-type tunnel layer 131,materials of the n-type tunnel layer 133, existence or non-existence ofthe highly n-type impurities-doped layer 132, and the distribution ofimpurity concentration in each of the p-type tunnel layer 131 and then-type tunnel layer 133.

First of all, materials of the p-type tunnel layer 131 will beexplained. In the Examples 1 to 3 and the Comparative Example, thep-type tunnel layer 131 is made of AlGaAs.

Then, materials of the n-type tunnel layer 133 will be explained. In theExamples 1 to 3, the n-type tunnel layer 133 is made of GaInP. On theother hand, the n-type tunnel layer 133 of the Comparative Example ismade of AlGaAs.

Then, existence or non-existence of the highly n-type impurities-dopedlayer 132 will be explained. In the Examples 1, 2 and the ComparativeExample, the highly n-type impurities-doped layer 132 is provided(described as “YES” in Table 2). On the other hand, the highly n-typeimpurities-doped layer 132 is not provided in the Example 3 (describedas “NO” in Table 2).

Finally, the distribution of impurity concentration in each of thep-type tunnel layer 131 and the n-type tunnel layer 133 will beexplained. In the Examples 1, 3 and the Comparative Example, theimpurity concentration in each of the p-type tunnel layer 131 and then-type tunnel layer 133 is made constant (see the middle section (thefirst example) in FIG. 2). On the other hand, in the Example 2, theimpurity concentration in each of the p-type tunnel layer 131 and then-type tunnel layer 133 is inclined (see the lower section (the secondexample) in FIG. 2).

As explained above, the material of the n-type tunnel layer 133 isdifferent between the Example 1 and the Comparative Example. Further,the distribution of impurity concentration in each of the p-type tunnellayer 131 and the n-type tunnel layer 133 is different between theExamples 1 and 2. Moreover, the highly n-type impurities-doped layer 132is present in the Example 1 while the highly n-type impurities-dopedlayer 132 is not present in the Example 3.

<Semiconductor Light-Emitting Element>

With these semiconductor layer forming substrates 1 of the Examples 1 to3 and the Comparative Example being used as a starting material, thesemiconductor light-emitting element 2 was manufactured using themanufacturing method shown in FIG. 6. The semiconductor light-emittingelement 2 thus obtained was subjected to various evaluations.

<Difference Due to the Material Constituting the n-Type Tunnel Layer>

FIG. 7 shows a relationship between a forward current IF and a lightemission output Po of the semiconductor light-emitting elements 2 of theExample 1 and the Comparative Example. In FIG. 7, the horizontal axisindicates the forward current IF (mA) and the vertical axis indicatesthe light emission output Po (mW).

It is understood from FIG. 7 that the light emission output Po of thesemiconductor light-emitting element 2 of the Example 1 is improved byabout 10% as compared to that of the semiconductor light-emittingelement 2 of the Comparative Example. Note that the light emissionoutput Po of the semiconductor light-emitting elements 2 of the Examples2 and 3 is also improved as compared to that of the semiconductorlight-emitting element 2 of the Comparative Example, although not shownin the figure.

From the above, it will be understood that the light emission output Pocan be improved by composing the n-type tunnel layer 133 of the tunneljunction layer 13 of a phosphide (GaInP), instead of an arsenide(AlGaAs).

<Difference Due to Impurity Concentration Distribution>

FIG. 8 shows a relationship between the light emission output Po and aforward voltage VF of the semiconductor light-emitting elements 2 of theExamples 1 and 2. Note that the light emission output Po and the forwardvoltage VF in the figure is a value when the forward current IF is 100(mA).

It is understood from FIG. 8 that the forward voltage VF of thesemiconductor light-emitting element 2 of the Example 2 is lower thanthat of the semiconductor light-emitting element 2 of the Example 1.However, it is also understood from the figure that the light emissionoutput Po of the semiconductor light-emitting element 2 of the Example 2is slightly lower than that of the semiconductor light-emitting element2 of the Example 1.

From the above, it will be understood that the forward voltage VF can bereduced by inclining the impurity concentration distribution in each ofthe p-type tunnel layer 131 and the n-type tunnel layer 133 of thetunnel junction layer 13.

<Difference Due to Existence or Non-Existence of the Highly n-TypeImpurities-Doped Layer>

FIG. 9A is a TEM picture of the tunnel junction layer 13 of the Example1, and FIG. 9B is a TEM picture of the tunnel junction layer 13 of theExample 3.

As shown in FIG. 9A, between the p-type tunnel layer 131 and the n-typetunnel layer 133 constituting the tunnel junction layer 13, anotherlayer, namely the highly n-type impurities-doped layer 132 is thought tobe present in the Example 1. On the other hand, as shown in FIG. 9B, thep-type tunnel layer 131 and the n-type tunnel layer 133 constituting thetunnel junction layer 13 seem to directly face each other in the Example3; the highly n-type impurities-doped layer 132 is thought not to bepresent.

FIG. 11 shows the results of secondary ion mass spectroscopy (SIMS) ofthe tunnel junction layers 13 of the Examples 1 and 3. The inventorsused IMS 7f-Auto from CAMECA and carried out measurement using thedynamic SIMS (D-SIMS) mode, which analyzes a target sample while erodingits surface. In FIG. 11, the horizontal axis indicates depth (nm) andthe vertical axis indicates concentration (atoms/cm³) of the n-typeimpurities (Te in this example). FIG. 11 also shows the results ofanalysis on the first p-type cladding layer 123 and the second n-typecladding layer 141, which are present above and below the tunneljunction layer 13. FIG. 11 also shows a positional relationship betweenthe first p-type cladding layer 123, the p-type tunnel layer 131, then-type tunnel layer 133 and the second n-type cladding layer 141estimated from the depth. Note that the positional relationship shown inthe figure is merely a guide, and may be slightly different from theactual one.

In the Example 1, the maximum concentration of the n-type impurities was1.6×10²⁰ (atoms/cm³). On the other hand, in the Example 3, the maximumconcentration of the n-type impurities was 3.0×10¹⁹ (atoms/cm³). Inother words, the maximum concentration of the n-type impurities in theExample 1 was of the order of 10²⁰ while that in the Example 3 was ofthe order of 10¹⁹.

FIG. 10 shows a relationship between the forward voltages VF of thesemiconductor light-emitting elements 2 of the Examples 1 and 3.Similarly to FIG. 8, the forward voltage VF shown in the figure is avalue when the forward current IF is 100 (mA).

It is understood from FIG. 10 that the semiconductor light-emittingelement 2 of the Example 1 has a lower voltage VF than the semiconductorlight-emitting element 2 of the Example 3.

From the above, it will be understood that the forward voltage VF can bereduced by providing, between the p-type tunnel layer forming process(step 50; the first process) and the n-type tunnel layer forming process(step 60; the third process), the process of supplying an n-typeimpurity material gas while stopping the supply of a group III materialgas and a group V material gas (the second process). It will also beunderstood that the forward voltage VF can be reduced by providing thehighly n-type impurities-doped layer 132 within the tunnel junctionlayer 13.

The foregoing description of the present exemplary embodiment of thepresent invention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Thepresent exemplary embodiment was chosen and described in order to bestexplain the principles of the invention and its practical applications,thereby enabling others skilled in the art to understand the inventionfor various embodiments and with the various modifications as are suitedto the particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

The invention claimed is:
 1. A light-emitting diode comprising: a firstlight-emitting part including a first p-type layer, a first n-typelayer, and a first active layer, the first p-type layer containing acompound semiconductor and p-type impurities, the first n-type layercontaining a compound semiconductor and n-type impurities, the firstactive layer containing a compound semiconductor and being sandwichedbetween the first p-type layer and the first n-type layer; a secondlight-emitting part including a second p-type layer, a second n-typelayer, and a second active layer, the second p-type layer containing acompound semiconductor and p-type impurities, the second n-type layercontaining a compound semiconductor and n-type impurities, the secondactive layer containing a compound semiconductor and being sandwichedbetween the second p-type layer and the second n-type layer, the secondlight-emitting part emitting light of the same wavelength as the firstlight-emitting part; and a tunnel junction part including a third p-typelayer and a third n-type layer, the third p-type layer facing the firstp-type layer and containing Al_(x)Ga_(1-x)As (0≤x≤0.3) and p-typeimpurities, the third n-type layer facing the second n-type layer andcontaining (Al_(x)Ga_(1-x))_(y)In_(1-y)P (0≤x≤0.2, 0.4≤y≤0.6) and n-typeimpurities, the tunnel junction part being sandwiched between the firstlight-emitting part and the second light-emitting part, the third p-typelayer and the third n-type layer forming a tunnel junction.
 2. Thelight-emitting diode according to claim 1, wherein the tunnel junctionpart further includes a highly n-type impurities-doped layer at aboundary between the third p-type layer and the third n-type layer, thehighly n-type impurities-doped layer containing n-type impurities at ahigher concentration than the third n-type layer.
 3. The light-emittingdiode according to claim 2, wherein the highly n-type impurities-dopedlayer is thinner than the third n-type layer and the third p-type layer.4. The light-emitting diode according to claim 2, wherein aconcentration of the n-type impurities in the highly n-typeimpurities-doped layer is not less than 1×10²⁰ cm⁻³ and not more than1×10²¹ cm⁻³.
 5. The light-emitting diode according to claim 1, wherein aconcentration of the n-type impurities in the third n-type layer ishigher at a side facing the third p-type layer than at a side facing thesecond n-type layer.
 6. The light-emitting diode according to claim 1,wherein a concentration of the p-type impurities in the third p-typelayer is higher at a side facing the third n-type layer than at a sidefacing the first p-type layer.
 7. The light-emitting diode according toclaim 1, wherein both of the first active layer and the second activelayer have a single- or multi-quantum well structure including a welllayer and a barrier layer, the well layer is composed of(Al_(x)Ga_(1-x))_(y)In_(1-y)As_(z)P_(1-z) (0≤x≤0.2, 0.7≤y≤1.0,0.7≤z≤1.0), and the barrier layer is composed ofAl_(x)Ga_(1-x)As_(z)P_(1-z) (0≤x≤0.3, 0.7≤z≤1.0).
 8. The light-emittingdiode according to claim 1, wherein each of the first p-type layer, thesecond p-type layer and the third p-type layer contains C as p-typeimpurities, and each of the first n-type layer, the second n-type layerand the third n-type layer contains Te as n-type impurities.
 9. Alight-emitting diode comprising: a first light-emitting part including afirst p-type layer, a first n-type layer, and a first active layer, thefirst p-type layer containing Al, Ga, As and p-type impurities, thefirst n-type layer containing Al, Ga, As and n-type impurities, thefirst active layer containing a group III-V semiconductor and beingsandwiched between the first p-type layer and the first n-type layer; asecond light-emitting part including a second p-type layer, a secondn-type layer, and a second active layer, the second p-type layercontaining Al, Ga, As and p-type impurities, the second n-type layercontaining Al, Ga, As and n-type impurities, the second active layercontaining a group III-V semiconductor and being sandwiched between thesecond p-type layer and the second n-type layer, the secondlight-emitting part emitting light of the same wavelength as the firstlight-emitting part; and a tunnel junction part including a third p-typelayer and a third n-type layer, the third p-type layer facing the firstp-type layer and containing Ga, As and p-type impurities, the thirdn-type layer facing the second n-type layer and containing Ga, In, P andn-type impurities, the tunnel junction part being sandwiched between thefirst light-emitting part and the second light-emitting part, the thirdp-type layer and the third n-type layer forming a tunnel junction. 10.The light-emitting diode according to claim 9, wherein the third n-typelayer has a larger band gap than the third p-type layer.
 11. Thelight-emitting diode according to claim 9, wherein the first p-typelayer and the second n-type layer have a common composition except forcontained impurities.
 12. The light-emitting diode according to claim 9,wherein each of the third p-type layer and the third n-type layer iscomposed of a direct band gap semiconductor.
 13. The light-emittingdiode according to claim 9, wherein a concentration of the n-typeimpurities in the third n-type layer is not less than 1×10²⁰ cm⁻³ andnot more than 1×10²¹ cm⁻³.